#include<stdio.h>
#include<math.h>
int main()
{
    float a,b,c,t;
    float s;
    printf("enter the length of three lines\n");
    scanf("%f%f%f",&a,&b,&c);
    s=(a+b+c)/2;
    t=sqrt(s*(s-a)*(s-b)*(s-c));
    printf("area is %f\n",t);

}